Oxytropism: a new twist in pollen tube orientation.

Chemical gradients and structural features within the pistil have been previously proposed as factors determining the directionality of pollen tube growth. In this study, we examine the behavior of pollen of eight species germinated in a dynamic oxygen gradient. While the germination rates of some species decreased directly with decreasing oxygen tension, other species showed no decrease in germination at oxygen tensions as low as 2 kPa. In one species, germination was consistently greater at decreased oxygen tensions than at ambient atmospheric levels. In three of the eight species tested, the developing pollen tube showed clear directional growth away from the more-oxygenated regions of the growth medium, while in one species growth was towards the more-oxygenated region. The remaining four species showed random tube growth. The pattern of oxytropic responses among the taxa suggests that this tropic behavior is both widespread and phylogenetically unpredictable.

A pseudoautosomal random amplified polymorphic DNA marker for the sex chromosomes of Silene dioica.

The segregation pattern of an 810-bp random amplified polymorphic DNA (RAPD) band in the F1 and backcross generations of a Silene dioica (L.) Clairv. family provides evidence that this molecular marker is located in the pseudoautosomal region (PAR) of the X and Y chromosomes. The marker was found through a combination of bulked segregant analysis (BSA) and RAPD techniques. Recombination rates between this pseudoautosomal marker and the differentiating portion of the Y chromosome are 15% in both generations. Alternative explanations involving nondisjunction or autosomal inheritance are presented and discussed. Chromosome counts provide evidence against the nondisjunction hypothesis, and probability calculations argue against the possibility of autosomal inheritance. This constitutes the first report of a pseudoautosomal DNA marker for plant sex chromosomes.

Confocal optical sectioning for meiotic analysis in Oenothera species and hybrids.

We present a photomicrographic technique for analysis of meiosis in Oenothera species and hybrids. In many species, the 14 isomorphic, 1-2 microns chromosomes are organized into a permanent translocation ring. Interspecific hybrid meiotic analysis is complicated by variations in homology between chromosome sets (Renner complexes) of allospecific origin. Though most wild species from complete rings of 14 at meiosis, hybrids often form combinations of smaller rings and bivalents. There is evidence that asynapsis (chain and univalents) also frequently occurs in hybrids. The greater complexity of hybrid meiotic organization can hinder resolution of individual chromosomes in such chains and small rings and encumber photomicrography of all chromosomes in a cell. Confocal laser scanning microscopy (CLSM) offers a new cytogenetic approach in ring-forming Oenothera species and hybrids. Fortunately, crystal violet, the stain classically used with this difficult material, fluoresces at an excitation wavelength of 488 nm and may thus be employed with the CLSM. Serial projection of image maxima from Z-axis confocal optical sections enables the investigator to count chromosomes and establish pairing relationships, regardless of chromosomal distribution.

The association between pollen size and Renner complex in Oenothera villaricae and O. picensis ssp. picensis and their hybrids: evidence for preanthesis pollen competition.

In both Oenothera villaricae Dietrich and O. picensis ssp. picensis, chromosomes are transmitted as two Renner complexes. Reciprocal combinations of the Renner complexes produce eight different F1 hybrids, but only seven are viable. Each species, and each F1 hybrid, produces three sizes of pollen, approximately 50% small sterile grains, 15% medium-sized viable grains and 35% large viable grains. Medium- and large-sized grains were separated manually and subjected to random amplified polymorphic DNAs (RAPDs) analysis. A pattern of RAPD amplifications was obtained which indicates that, for each species and F1 hybrid, one specific Renner complex characterizes the medium- and another the large-sized viable pollen. The results indicate that pollen size is determined in part by the pollen genotype and in part by the genotype of the other pollen grains developing within the same anther.

Pollen-pistil interaction in maize: effects on genetic variation of pollen traits.

Various factors (pollen diameter, in vitro germination and tube length, in vivo growth rate in selfed and nonselfed styles) which could possibly contribute to the competitive ability of pollen were investigated on 30 Zea mays L. inbred lines. The only factor with which pollen diameter was positively correlated was in vitro pollen-tube growth. Traits related to the early stages of growth (in vitro germination, in vitro tube length, early in vivo pollen growth rate) were all positively correlated with each other, and these early characteristics were negatively correlated with late in vivo tube growth rate, which is largely influenced by the stylar genotype.

Confocal laser scanning microscopy of mitochondria within microspore tetrads of plants using rhodamine 123 as a fluorescent vital stain.

The present study demonstrates that rhodamine 123 penetrates the callose walls surrounding plant microspores before they are released from tetrads. The stain accumulates in active mitochondria due to the electrical potential across the mitochondrial membrane. Accumulation of dye does not occur in mitochondria of fixed cells and fades quickly when mitochondrial activity is inhibited by exposure to carbonyl cyanide m-chlorophenyl hydrazone. Rhodamine can be used as a viability test for microspores still within tetrads, thus making it possible to determine when during development genes leading to pollen sterility are expressed. Rhodamine 123 is excited by blue (550 nm) light and can thus be used with confocal laser scanning microscopy. Anthers of Nicotiana tabacum, Oenothera villaricae, Silene dioica and Lycopersicum esculentum were studied here.

Comparison of the response to aluminum toxicity in gametophyte and sporophyte of four tomato (Lycopersicon esculentum Mill.) cultivars.

We tested pollen from four tomato cultivars differing in sensitivity to aluminum in the sporophyte to determine if Al sensitivity was also expressed in pollen. Pollen sensitivity to Al was measured by the ability to germinate and grow in a control solution after a short period in a high concentration of Al. The response was ranked and compared to the Al sensitivity ranking of the four cultivars based on top growth in Al toxic soil. In addition, seedlings from the most and least sensitive cultivars, based on pollen germination, were compared for Al sensitivity in nutrient solutions. Treatment with Al significantly reduced pollen germination in the two more sensitive cultivars, but not in the two more resistant cultivars. However, the ranking was not the same as that based on the shoot growth of the sporophyte. Root growth as a criterion of sporophytic Al sensitivity produced results similar to pollen germination. The study suggests that although the correspondence is better for some phenotypic responses of the sporophyte than others, Al tolerance appears to be another character expressed in both pollen and sporophyte.

Correlations between gametophytic (pollen) and sporophytic (seed) generations for polyunsaturated fatty acids in oilseed rape Brassica napus L.

Lipids were extracted from the diploid seed and haploid pollen of Brassica napus L. Two fractions of pollen lipids, namely the diploid-specified pollen-coat and the haploid-specified internal cytoplasmic lipids were obtained. Significant correlations exist between pollen and seed generations for linoleic (18∶2) and linolenic (18∶3) acids. In pollen internal storage lipids, the level of 18∶3 is positively correlated and the level of 18∶2 is negatively correlated with the level of 18∶3 in seed lipids. Evidence is presented that strongly supports the hypothesis that lipid biosynthesis occurs within the pollen and that synthesis is specified by haploid genes. These data support the concept of pollen selection, so that selecting among living pollen grains for superior individuals has potential as a new plant breeding tool for improving seed oil quality.

The parallel expression of metal tolerance in pollen and sporophytes of Silene dioica (L.) Clairv., S. alba (mill.) krause and Mimulus guttatus DC.

The purpose of this paper was to determine if heavy metal tolerance was expressed in pollen and if its expression was correlated with the tolerance of the pollen source. Clones of Silene dioica, tolerant to zinc, closely related but nontolerant S. alba and clones of Mimulus guttatus tolerant and sensitive to copper were grown in the greenhouse in either standard potting soil or nutrient culture. Pollen was collected shortly after dehiscence, hydrated, and tested over a broad range of metal concentrations. The tolerance of the pollen source was determined by comparing root growth in solutions with and without heavy metals. In both Silene species and M. guttatus, the tolerance of the parental clone was expressed in its pollen. Pollen from tolerant individuals was able to germinate and grow at concentrations of metals which markedly inhibited pollen from nontolerants.

A family outbreak of toxoplasmosis: a serendipitous finding.

A family outbreak of toxoplasmosis involving five members of a Lebanese family is described. We believe it to be the first reported outbreak of toxoplasmosis in Australia. Kibbi , a traditional Lebanese dish which can occasionally incorporate raw meat, may have been the source of infection. The chance occurrence of an outbreak of hepatitis A in the same family subsequently led us to discover this outbreak.

Gametophytic self-incompatibility reexamined.

The conventional hypothesis of gametophytic self-incompatibility in the angiosperms involves one to four multiallelic incompatibility loci and the positive inhibition of incompatible pollen tubes. However, this concept does not accommodate recent experimental data indicating that there may be many loci. An alternative hypothesis which incorporates many loci and complementary pollen-style interactions suggests that there may be no S gene, as previously thought, and that gametophytic self-incompatibility is perhaps merely one aspect of extensive pollen-style interactions.

A report of a spring-summer outbreak of echovirus II infection.

A spring-summer epidemic of echovirus II in New South Wales, Australia, is reported. The symptomatology was found to be age dependent. Neonates and young infants tended to have a severe 'septicaemic' illness. Older infants had a variety of clinical presentations: aseptic meningitis, febrile convulsions, upper respiratory tract infections, and acute enteritis. Children over the age of two in this study uniformly presented with symptoms suggestive of aseptic meningitis--confirmed by cerebrospinal (CSF) cytology in the majority of cases. The clinical presentation of an acute febrile illness in the young child may not allow for distinction between bacterial and viral infection. The importance of the recognition and confirmation of a viral aetiology relates to the subsequent management: i.e. antibiotics may be withheld, hospitalisation may be shortened, and a more favourable prognosis can be made. Certain epidemiological clues and laboratory studies are helpful in suggesting a viral aetiology, but a definitive diagnosis of enteroviral infection may only be readily achieved by virus isolation in tissue culture.

A two-part study of the aetiological role of rotavirus in intussusception.

The aetiology of intussusception is ill-defined, with viruses being incriminated as one of many possible aetiological agents. A two-part study was performed by us to investigate the aetiological role of rotavirus in intussusception. Retrospective epidemiological data revealed a negative correlation between the incidence of rotaviral gastroenteritis and the incidence of intussusception. A prospective investigation employing electronmicroscopy, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence studies of faeces and fluorescent antibody studies of sera demonstrated evidence of rotavirus infection in only 2 of 24 children with intussusception. No evidence was forthcoming in this study of an aetiological role of rotavirus in intussusception.

Pollen tetrads in the detection of environmental mutagenesis.

Although pollen viability promises to be a very sensitive indicator of environmental mutagenesis, its utility in this regard is confounded by the fact that it is influenced also by nonmutagenic environmental stress. However, with appropriately homozygous material, we may discriminate between mutagenic and nonmutagenic influences on pollen viability. Pollen inviability resulting from mutagenesis will exhibit a strong tendency to segregate, whereas stress induced inviability will not. When pollen grains are shed individually, evidence for genetic segregation is often lost, but with pollen in tetrads, this evidence, a specific indicator of environmentally induced mutation, is preserved. A further advantage of pollen in tetrads is that, again because evidence for genetic segregation is preserved, tetrads allow us to distinguish between pre- and postpachytene mutations. This capability eliminates the problem of mutant sectors whereby a single mutational event may give rise to a large number of mutant cells. Methods of examining pollen tetrads are discussed.

Pollen Tube Growth Rates in Zea mays: Implications for Genetic Improvement of Crops.

Speed of pollen tube growth is positively correlated with the quality of the resultant sporophytic generation. Therefore, gametophytic competition may be an important adaptive mechanism. Furthermore, pollen tube growth rates may be used to predict the quality of F(1) crosses in crop species.

The rise of the angiosperms: a genecological factor.

In the primitive angiosperms, closed carpels are believed to have evolved as protection for ovules, which would otherwise be injured by animal pollinators. The hypothesis is presented that, whatever the origin and other functions of angiosperms, insect pollination and closed carpels may, in combination, reduce the influence of random variation on pollen tube competition, thus enhancing the ability of natural selection to act on the gametophytic phase of the life cycle. The microgametophytic phase represented by vast numbers of haploid individuals can then serve, by insect pollination and closed carpels, as a screen against any genome not functioning with a high degree of metabolic vigor. Poorly balanced genomes could thus be eliminated at relatively little cost. Insect-pollinated angiosperms would therefore benefit from positive aspects of sexual recombination. Such a system may have allowed the angiosperms to undergo their rise to dominance.

Self-incompatibility systems as bioassays for mutagens.

Many flowering plants are unable to set seeds with their own pollen because a system known as gametophytic self-incompatibility is operating. The basis of this system is a single multiallelic locus S, and if the S allele carried by a pollen grain matches one of the two S alleles carried in the style, as it is certain to do upon self-pollination, then pollen tube growth is inhibited. Should one of the self-pollen grains carry a mutated S allele, however, it would not match either of those carried in the style and would therefore, not be inhibited. Gametophytic self-incompatibility thus provides a mechanism for discriminating between such mutant and nonmutant pollen grains. Knowing the numbers of pollen grains available to the stigma, and also the numbers of seeds produced, it becomes possible to estimate the frequency with which mutations occur at the S locus. Assay systems of mutagenesis which employ gametophytic self incompatibility will allow very large numbers of pollen grains to be screened for S allele mutants, which should indicate the mutagenicity of the environment. These systems have the added benefit that screening is done by the stylar tissues, rather than technicians. Finally, they may be used to construct largely autonomous assay systems which would provide continuous monitoring of the environment.

Male gametophyte in maize: II. Pollen vigor in inbred plants.

The competitive ability of pollen from inbred plants in mixed pollinations in this study is not merely maintained but enhanced through successive generations of selfing. The data presented suggest two conclusions: 1) the possible existence of pollen-stylar interactions during successive selfings, which select for certain pollen genotypes, those best suited for rapid growth through "self" styles; and 2) the presence of sporophytic vigor in the heterotic F1 sporophyte, or its absence in the "depressed" F7 sporophyte, is not necessarily demonstrated in the gametophytic generation, perhaps because it can be overwhelmed by other factors, e.g. gametophytic response to selection.